FIGS. 1A, 1B and 1C show a configuration of an electrical-optical hybrid connector described in Patent literature 1 as an example of an electrical-optical hybrid connector of this type comprising a plug and a receptacle. FIG. 1A shows the plug, FIG. 1B shows the plug partially disassembled, and FIG. 1C shows the receptacle.
A plug 10 has an insulating main body 11 and a plug terminal mounted on the insulating main body 11. The insulating main body 11 has a base part 13 having a fitting surface 13a and a tongue piece 14 extending forward from the base part 13. A through hole for housing an optical fiber is formed in the base part 13. A lens 15 is housed in the through hole and disposed so as to protrude from the fitting surface 13a. 
A metal shell 12 is disposed to surround the insulating main body 11. An upper housing space 16 and a lower housing space 17 are formed between the tongue piece 14 and a top plate of the metal shell 12 and between the tongue piece 14 and a bottom plate of the metal shell 12, respectively.
The plug terminal includes a plurality of first terminals and a plurality of second terminals. The first terminals 18 are mounted on the upper surface of the tongue piece 14 and are exposed in the upper housing space 16. Although not visible in FIG. 1B, the second terminals are mounted on the lower surface of the tongue piece 14 and are exposed in the lower housing space 17.
A receptacle (socket) 20 has an insulating main body 21, a socket terminal mounted on the insulating main body 21, and a metal shell 22 that covers the insulating main body 21. The insulating main body 21 has a housing space 23 for housing the plug 10, a base part 24, and a first tongue piece 25 extending forward from the base part 24.
The socket terminal includes a plurality of first terminals and a plurality of second terminals. First terminals 26 are disposed on the lower surface of the first tongue piece 25. The insulating main body 21 has a second tongue piece 27 extending forward from the base part 24 disposed in parallel with the first tongue piece 25. Second terminals 28 are disposed on the upper surface of the second tongue piece 27.
A through hole is formed through the first tongue piece 25 and the base part 24. A lens 29 is held in the through hole and positioned at a tip end part of the first tongue piece 25. An optical fiber is housed behind the lens 29 in the through hole.
The receptacle 20 has two, upper and lower, sets of the housing space 23, the first tongue piece 25, the second tongue piece 27, the first terminals 26 and the second terminals 28.
With the electrical-optical hybrid connector comprising the plug 10 and the receptacle 20, when the plug 10 is inserted into the receptacle 20, the first terminals 18 of the plug 10 are connected to the first terminals 26 of the receptacle 20, and the second terminals of the plug 10 are connected to the second terminals 28 of the receptacle 20. In addition, the lens 15 of the plug 10 is inserted into the through hole of the receptacle 20, in which the lens 29 is positioned, to face the lens 29 and establish an optical connection (transmission of optical signals).